Metal ion catalysis of the decomposition of transient 2-carboxy-2,5-cyclohexadienones in aqueous solution

1988 ◽  
Vol 66 (5) ◽  
pp. 1194-1198 ◽  
Author(s):  
Oswald S. Tee ◽  
N. Rani Iyengar
Keyword(s):  
Aqueous Solution ◽  
Carboxylic Acid ◽  
Metal Ion ◽  
Hydrogen Ion ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Ferric Ions ◽  
Bromide Ion ◽  
Metal Ion Catalysis ◽  
The Stability

Bromide ion induced debromination of the anion of 4-bromo-4-methyl-2,5-cyclohexadienone-2-carboxylic acid (1) is catalyzed by cupric ions and ferric ions. Similarly, the enolization of the anion of the benzocyclohexadienone 3, which is formed during the bromination of 1-naphthol-2-carboxylic acid, is catalyzed by some metal ions. The origin of the catalysis in these reactions is strong metal ion binding to the incipient dianion products that are of the salicylate type. Evidence for this is that the efficiency of the metal (and hydrogen) ion catalysis parallels the stability of the analogous complexes with the salicylate dianion.

scholarly journals Metal Ion-Binding Properties of the Diphosphate Ester Analogue, Methylphosphonylphosphate, in Aqueous Solution

1999 ◽  
Vol 6 (6) ◽  
pp. 321-328 ◽  
Author(s):  
Bin Song ◽  
Jing Zhao ◽  
Fridrich Gregáň ◽  
Nadja Prónayová ◽  
S. Ali A. Sajadi ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Minor Role ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Ph Titration ◽  
Role Based ◽  
The Stability ◽  
A Minor ◽  
Complex Stabilities

The stability constants of the 1:1 complexes formed between methylphosphonylphosphate (MePP3-), CH3P(O)2--O-PO32- , and Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+,​ or Cd2+ (M2+) were determined by potentiometric pH titration in aqueous solution (25 C° ; l = 0.1 M, NaNO3 ). Monoprotonated M(H;MePP) complexes play only a minor role. Based on previously established correlations for M2+ -diphosphate monoester complex-stabilities and diphosphate monoester β-group. basicities, it is shown that the M(Mepp)- complexes for Mg2+ and the ions of the second half of the 3d series, including Zn2+ and Cd2+, are on average by about 0.15 log unit more stable than is expected based on the basicity of the terminal phosphate group in MePP3-. In contrast, Ba(Mepp)- and Sr(Mepp)- are slightly less stable, whereas the stability for Ca(Mepp)- is as expected, based on the mentioned correlation. The indicated increased stabilities are explained by an increased basicity of the phosphonyl group compared to that of a phosphoryl one. For the complexes of the alkaline earth ions, especially for Ba2+, it is suggested that outersphere complexation occurs to some extent. However, overall the M(Mepp)- complexes behave rather as expected for a diphosphate monoester ligand.

Metal Ion-Binding Properties in Aqueous Solution of the Nucleoside Analogue, 5,6-Dichloro-1-(β-ᴅ-ribofuranosyl)benzimidazole (DRB)

1998 ◽  
Vol 53 (8) ◽  
pp. 903-908 ◽  
Author(s):  
Larisa E. Kapinos ◽  
Bin Song ◽  
Helmut Sigel
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Ion Binding ◽  
Acidity Constant ◽  
Metal Ion Binding ◽  
Binding Properties ◽  
Straight Line ◽  
Data Points ◽  
The Stability ◽  
Straight Lines

Abstract The stability constants of the 1:1 complexes formed between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ or Cd2+ (= M2+) and 5,6-dichloro-l-(β-ᴅ-ribofuranosyl)benzim idazole (DRB) were determined by potentiom etric pH titrations in aqueous solution (25 °C; I = 0.5м, NaNO3). The acidity constant of H(DRB)+, the proton being at N3, was measured by the same method and the result was confirmed via spectrophotometry. Based on previously established [L. E. Kapinos, B. Song, H. Sigel, Inorg. Chim . Acta 280, in press (1998)] logммʟ versus Kʜʜʟ straight-line plots for complexes of imidazole-type ligands it is shown for the Mn(DRB)2+ and Zn (DRB)2+ complexes, as examples, that the benzene ring of the benzim idazole residue exerts a steric inhibition for metal ion binding at N3; i.e., the data points for the M(DRB)2+ complexes fall clearly below the straight lines defined by the imidazole- type ligands.

Metal Ion-Binding Properties of the Nucleotide Analogue 1-[2-(Phosphonomethoxy)ethyl]cytosine (PMEC) in Aqueous Solution

1999 ◽  
Vol 64 (4) ◽  
pp. 613-632 ◽  
Author(s):  
Claudia A. Blindauer ◽  
Antonín Holý ◽  
Helmut Sigel
Keyword(s):  
Aqueous Solution ◽  
Metal Ions ◽  
Metal Ion ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Binding Properties ◽  
Nucleotide Analogue ◽  
Ether Oxygen ◽  
The Stability ◽  
Isomeric Equilibria

The acidity constants of the twofold protonated nucleotide analogue 1-[2-(phosphonomethoxy)ethyl]cytosine, H2(PMEC)±, as well as the stability constants of the M(H;PMEC)+ and M(PMEC) complexes with the metal ions M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ have been determined by potentiometric pH titrations in aqueous solution at I = 0.1 M (NaNO3) and 25 °C. Comparison with previous results for the nucleobase-free compound (phosphonomethoxy)ethane, PME, and the parent nucleotides cytidine 5'-monophosphate (CMP2-) and 2'-deoxycytidine 5'-monophosphate (dCMP2-) shows that the metal ion-binding properties of PMEC2- resemble closely those of PME2-: This means, the primary binding site is the phosphonate group and with all of the metal ions studied, 5-membered chelates involving the ether oxygen of the -CH2-O-CH2-PO32- chain are formed. The position of the isomeric equilibria between these chelates and the "open" complexes, -PO32-/M2+ is calculated; the degree of formation of the chelates is identical within the error limits for the M(PME) and M(PMEC) systems. Hence, like in M(CMP) and M(dCMP) no interaction occurs with the cytosine residue in the M(PMEC) complexes. However, the monoprotonated M(H;PMEC)+ as well as the M(H;CMP)+ and M(dCMP)+ species carry the metal ion predominantly at the nucleobase, while the proton is at the phosph(on)ate group. The coordinating properties of PMEC2- and CMP2- or dCMP2- differ thus only with respect to the possible formation of the 5-membered chelates involving the ether oxygen in M(PMEC) species, a possibility which does not exist in the complexes of the parent nucleotides. Possible reasons why PMEC is devoid of a significant antiviral activity are shortly discussed.

Properties of the Ternary (Dien)Pt(PMEA-N7) Complex Containing Diethylenetriamine (Dien) and the Antiviral 9-[2-(Phosphonomethoxy)ethyl]adenine (PMEA). Synthesis, Biological Screening, Acid-Base Behaviour, and Metal Ion-Binding in Aqueous Solution

2000 ◽  
Vol 55 (12) ◽  
pp. 1141-1152 ◽  
Author(s):  
Gunnar Kampf ◽  
Marc Sven Lüth ◽  
Jens Müller ◽  
Antonín Holý ◽  
Bernhard Lippert ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Metal Ions ◽  
Metal Ion ◽  
Ion Binding ◽  
Uv Spectrophotometry ◽  
Metal Ion Binding ◽  
Ph Titration ◽  
Complex Species ◽  
Ether Oxygen ◽  
The Stability

The synthesis of (Dien)Pt(PMEA-N7), where Dien = diethylenetriamine and PMEA2- = dianion of 9-[2-(phosphonomethoxy)ethyl]adenine, is described. No useful biological activity could be discovered for this complex which is in contrast to the known antiviral properties of PMEA itself. The acidity constants of the twofold protonated H2[(Dien)Pt(PMEA-N7)]2+ complex were determined (UV spectrophotometry and potentiometric pH titration): The release of the proton from the -P(O)2(OH)- group is only slightly affected by the N7-coordinated (Dien)Pt2+ unit, whereas the acidity of the (N1)H+ site is strongly enhanced. The stability constants of the M[(Dien)Pt(PMEA-N7)]2+ complexes with the metal ions M2+ = Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ were measured by potentiometric pH titrations in aqueous solution at 25 °C and I = 0.1 M (NaNO3). Application of previously determined straightline plots of log KM(R-PO3)M versus KH(R-PO3)H for simple phosph(on)ate ligands, R-PO32- where R represents a non-inhibiting residue without an affinity for metal ions, proves that the primary binding site of the complex-ligand, (Dien)Pt(PMEA-N7), with all the metal ions studied is the phosphonate group; in most instances the expected stability is actually reduced by about 0.4 log units due to the N7-bound (Dien)Pt2+ unit. Only for the Cu[(Dien)Pt(PMEA-N7)]2+ and the Zn[(Dien)Pt(PMEA-N7)]2+ systems the formation of some 5-membered chelates involving the ether oxygen atom of the -CH2-O-CH2-PO32- residue could be detected; the formation degrees are 52 ± 9% and 32 ± 14%, respectively. The metal ion-binding properties of (Dien)Pt(PMEA-N7) differ considerably from those of PMEA2-, yet they are relatively similar to those of pyrimidine-nucleoside 5'-monophosphates. The structures of the various complex species in solution are discussed and compared.

Transferrin binding of Al3+ and Fe3+.

1987 ◽  
Vol 33 (3) ◽  
pp. 405-407 ◽  
Author(s):  
R B Martin ◽  
J Savory ◽  
S Brown ◽  
R L Bertholf ◽  
M R Wills
Keyword(s):  
Stability Constant ◽  
Blood Plasma ◽  
Stability Constants ◽  
Metal Ion ◽  
Equilibrium Dialysis ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Quantitative Studies ◽  
Intensity Changes ◽  
The Stability

Abstract An understanding of Al3+-induced diseases requires identification of the blood carrier of Al3+ to the tissues where Al3+ exerts a toxic action. Quantitative studies demonstrate that the protein transferrin (iron-free) is the strongest Al3+ binder in blood plasma. Under plasma conditions of pH 7.4 and [HCO3-]27 mmol/L, the successive stability constant values for Al3+ binding to transferrin are log K1 = 12.9 and log K2 = 12.3. When the concentration of total Al3+ in plasma is 1 mumol/L, the free Al3+ concentration permitted by transferrin is 10(-14.6) mol/L, less than that allowed by insoluble Al(OH)3, by Al(OH)2H2PO4, or by complexing with citrate. Thus transferrin is the ultimate carrier of Al3+ in the blood. We also used intensity changes produced by metal ion binding to determine the stability constants for Fe3+ binding to transferrin: log K1 = 22.7 and log K2 = 22.1. These constants agree closely with a revision of the reported values obtained by equilibrium dialysis. By comparison with Fe3+ binding, the Al3+ stability constants are weaker than expected; this suggests that the significantly smaller Al3+ ions cannot coordinate to all the transferrin donor atoms available to Fe3+.

Self-assembly with fluorescence readout in a free base dipyrrin–polymer triggered by metal ion binding in aqueous solution

2019 ◽  
Vol 43 (24) ◽  
pp. 9711-9724 ◽  
Author(s):  
Rui Liu ◽  
Pothiappan Vairaprakash ◽  
Jonathan S. Lindsey
Keyword(s):  
Aqueous Solution ◽  
Self Assembly ◽  
Metal Ion ◽  
Zinc Ion ◽  
Ion Binding ◽  
Free Base ◽  
Metal Ion Binding

Profound morphological and fluorogenic changes ensue upon binding of a zinc ion by two polymers, each of which bears a single dipyrrin at one terminus, forming the bis(dipyrrinato)Zn(ii) complex.

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